Natural and anthropogenic impacts on dissolved inorganic carbon (DIC) within an urban river, Nanming River in southwestern China, were investigated using hydrochemistry and carbon isotopic compositions of dissolved inorganic carbon (delta C-13(DIC)). Because of the anthropogenic inputs, generally, the TDS values and major ionic compositions showed an increasing trend along the mainstream. The TDS values and most of the dissolved solutes compositions showed a dilution effect during storms, but the dilution effect did not strictly follow the theoretical dilution curve. Lighter delta C-13(DIC) values in the river after a rainstorm reflected the influx of rain water with biological CO2 during the rain event. Meanwhile, the negative relationship between delta C-13(DIC) values and dissolved inorganic carbon concentrations in the mainstream at different sampling campaigns suggested significant degradation of organic matter in the riverine channels. The variabilities of DIC in an urban river were mainly impacted by biological activities and infiltration of soil carbon dioxide. This study demonstrated that hydrological events and anthropogenic inputs are the main controls on the variations of dissolved solutes compositions and the DIC dynamics for an urban river.

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